The present invention relates to transfer apparatus for an alternating current (AC) electric power generator having at least two voltage regulators for supplying excitation to a field winding of the generator to regulate its voltage. The transfer apparatus is so-named because it transfers the function of regulating the generator output from one to another of the voltage regulators either manually or automatically. The invention also relates to the regulators combined with the transfer apparatus, which combination is called regulating apparatus herein. The invention also involves methods of operating the transfer apparatus.
A generator of electrical power such as an alternator or rotary exciter typically has a field winding the direct current (DC) energization of which sets up a magnetic field in the generator and thereby controls its AC output voltage. A prime mover turns a rotor of the generator, and mechanical energy is converted into electrical energy for electrical power lines to a load in a conventional manner. The rotor speed (rpm) of the generator determines the AC frequency of its output. The AC output voltage is regulated by a voltage regulator such as a shunt static exciter (SSE) which senses the generator AC voltage and varies the DC current in the generator field winding to maintain the generator output voltage level.
For demanding applications, such as naval shipboard generator installations for example, the need for the highest possible reliability of electric power has led to a need for a redundant voltage regulator scheme having at least two voltage regulators per generator. It has been known to connect two voltage regulators through diodes to the same field winding of a single generator. One voltage regulator was set to regulate the generator to a higher voltage than that for which the second regulator was set. In case the first regulator failed off, the second regulator could take over, albeit at a lower voltage. If either regulator failed on, an overvoltage in the generator output was detected, and the regulator conducting current at the time was shut off by removing its power.
When generators are connected in parallel, however, a voltage regulator failure does not necessarily cause an overvoltage in its associated generator output. Consequently, transfer and regulating apparatus and methods are needed that are compatible with multiple generator installations. Transfer apparatus and regulating apparatus should automatically reduce generator output when frequency falls, while maintaining the effectiveness of various monitoring and transferring features. Because of the importance of highly reliable power availability in particular applications, the art is also seeking new and improved types of transfer and regulating apparatus and methods capable of automatically detecting failures in particular circuits of each regulator. Apparatus and methods are needed to monitor the performance of the regulators and initiate a changeover, or transfer, from one regulator to another by solid state means without lowering the generator voltage as a result. Apparatus is also needed which is sufficiently intelligent to avoid improvidently transferring from one regulator to another due to problems external to the regulators.